Nowadays light emitting diodes (LED) are widely used in a variety of applications, such as indicator lamps, general lighting, automotive lighting, and advertising. In addition, video displays and sensors are also to be developed by LED devices. With the development of LEDs, the devices are subject to junction temperatures and current densities. These tend to cause excessive thermal stresses on the material, and may cause light-output degradation as most of the inputted power is converted to heat. Under this circumstance, the LED light performance is very much affected by temperature.
In general, thermal testing of LED devices is to measure the temperature rise, so as to ensure that the maximum junction temperature is not exceeded. The thermal resistance is defined as a property of the junction temperature of an LED device. Consequently, the thermal resistance is a critical parameter for evaluating a heat dissipation performance of an LED device. The conventional thermal measurement methods of LED devices are similar to those of general IC chips. The conventional methods for measuring LED thermal characteristics include two steps. The conventional LED thermal measurement methods begin with the first step of measuring a temperature sensitive parameter (TSP). A heating current, such as 300 mA, is provided to an LED device by a current source, and a voltage meter is used for measuring a relation between a temperature and an output voltage. Subsequently, the heating current is switched to a small current, such as 1 mA. A forward voltage under the small current is measured as the calculation of the device temperature. These steps are repeated many times. Moreover, there are some other conventional LED thermal measurement technologies, which are used for measuring the thermal resistance. Overall, these conventional thermal measurement methods are usually complicated and very time-consuming, and these aforesaid methods for measuring the accurate thermal resistance are all restricted due to the TSP value measurement, requiring a steady-state testing condition. Therefore, these thermal measurement methods or approaches require a longer time to monitor temperature at equilibrium, and are not suitable for fast measurement of thermal resistances and thermal electric characteristics of LED devices under different temperatures.
Accordingly, it is necessary to provide a method for measuring a thermal characteristic and a chip temperature of an LED device in a fast manner.
The above-described deficiencies of today's LED thermal measurement are merely intended to provide an overview of some of the problems of the conventional methods, and are not intended to be exhaustive. Other problems with conventional methods and corresponding benefits of the various non-limiting embodiments described herein may become further apparent upon review of the following description.